Synthesis Of Rare Earth Doped CaF 2 Luminescent Materials And Their Application In Bioassay

With the rapid development of modern biomedicine,bio-analytical technology,such as fluorescence analysis technology and bio-imaging technology,has been an important research tool.Bio-label materials have been focused on by researches in the fields of chemistry,materials and biology,because of the extensive application of fluorescence analysis and bio-imaging technologies.Organic dyes,semiconductor quantum dots,rare earth nanoparticles and so on are currently applied for fluorescence analysis technology and bio-imaging technology as luminescent bio-label materials.Due to the unique electron structure of rare earth elements,luminescent rare earth nanoparticles are of photo-physical properties of monochrome,long fluorescence lifetime and high PL intensity.And with advantages of high chemical stability and the low toxicity,luminescent rare earth nanoparticles,which can be easily connected with biomolecules by the surface modification,are an ideal bio-label materials.In this paper,high performance monodisperse luminescent CaF₂:Eu³⁺ nanocrystals with cubic phase were synthesized by thermal decomposition of organic precursors of trifluoroacetates of rare earth and calcium.And liuninescent CaF₂:Eu³⁺ nanocrystals were characterized by transmission electron microscopy（TEM）,polycrystalline powder X-ray diffraction（XRD）,UV-visible absorption spectra and fluorescence emission spectra etc..Morphology,structure and luminescence properties of CaF₂:Eu³⁺ nanocrystals were studied in details by the reaction temperature and the ratio of doping Eu³⁺.With the change of the temperature and the synthetic method,the particle size of as-prepared CaF₂:Eu³⁺nanocrystals is about 2 nm-15 nm.Their PL emission peaks are 590.nm and 612nm,respectively,corresponding to the 5D0→7FI transition and 5D0→77F₂ transition of Eu³⁺.Charge transfer band appeared from 400 nm to 560 nm,where broadening and red shift showed significantly.With the increase of the Eu³⁺ ion doped concentration up to 40%until the luminescent quenching concentration,the PL emission intensity increases and their fluorescence lifetime is ranged from 2 ms to 4 ms.Monodisperse cubic-phase CaF₂:Yb³⁺/Er³⁺,CaF₂:Yb³⁺/Tm³⁺ and CaF₂:Yb³⁺/Er³⁺/Tm³⁺nanocrystals were synthesized by thermal decomposition method,and their diameter was about 12 nm.All of them could be well dispersed in cyclohexane.With the laser irradiation of 980 nm,the upconversion fluorescence of those nanocrystals was bright and strong.When Er³⁺ was doped,upconversion fluorescence spectra of nanocrystals show characteristic emission of 540 nm and 650 nm.When Tm³⁺ was doped,upconversion fluorescence spectra of nanocrystals show characteristic emission of 475 nm and 800 nm.And the fluorescence lifetime of upconversion nanocrystals was longer than 70 μsAt R.T.,the surface modification of RE-doped CaF₂ nanocrystals was done by the Oxidation.TEM,TGA,contact angle,FT-IR spectroscopy and fluorescence emission spectra of CaF₂:Yb³⁺/Tm³⁺ nanocrystals were characterized before and after surface modification.With the Oxidation process,the composition,structure,morphology and optical properties of CaF₂:Yb³⁺/Tm³⁺ nanocrystals was no significant change,and the double bond on oleic acid molecular chain was oxidized to aldehyde.The measured aldehyde content was about 35%of the total surface ligands of CaF₂:Yb³⁺/Tm³⁺nanocrystals.And then,CaF₂:Yb³⁺/Tm³⁺@BSA nanoparticles were prepared by the coupling between bovine serum albumin（BS A）and aldehyde groups.After incubated with L02 hepatocytes,the cytotoxicity evaluation and the upconversion laser scanning confocal microscopic imaging nanoparticles were conducted with CaF₂:Yb³⁺/Tm³⁺@BSA nanoparticles.